Ing-surfaces



UNITED STATES PATENT OFFICE.

JOSEPH BROWN, OF LONDON, ENGLAND.

IMPROVEMENT IN COMPOSITIONS FOR SUPPORTING METALLIC PLATES FOR THEFORMATION OF PRINT- ING-SURFACES.

Specification forming part of Letters Patent No. 204,795, dated June ll,1878; application filed July 12, 1875.

To all whom it may concern:

Be it known that I, JOSEPH BROWN, of London, England, have invented anImproved Composition for Supporting Metallic Plates for the Formation ofDesigns, of which the following is a specification:

This invention relates to an improved process of forming matrices ofdesigns for the production of electrotype-plates directly by the hand ofthe artist or designer, in which the design is produced by means of apointed tool upon a thin sheet of soft metal supported upon a peculiarbacking of semi-plastic inelastic material, of sufficient body orconsistence to support the metal in the absence of pressure, butsufficiently yielding to give to the slightest touch of the artist, andallow the material to be depressed under the tool for the formation ofthe lines of design.

In carryin g out my invention, I take a composition of plaster-of-paris,one pound, chromate of potassa, one-quarter of an ounce, and

' common salt, one ounce, which forms a compound that will give to themost delicate touch of the artist, and will allow the finest lines to beproduced upon the metal by the tool. These ingredients may be mixed invarious proportions, which will depend somewhat upon the boldness ordelicacy of the design to be produced. The mixture may be brought to asemi-plastic state by the addition of about one pint of water, orsufficient to bring it to the proper consistence, and the plasticity ofthe compound may be modified to suit various re quirements by using moreor less water.

The semi-plastic composition is molded or otherwise formed into a flattablet of suitable size, and a sheet of soft metal is carefully securedupon the upper face of the same, projecting edges being left, which areafterward turned down over the sides of the tablet. The metal is thenready for the artist, who, with a pointed tool or tools, produces thedesired design by indenting the lines thereon. Whenever touched by thetool the metal will be depressed into the backing, which is of justsufficient body to support the untouched parts, but yields to theslightest pressure upon the tool. When the design is finished the metalis carefully removed from the backing, having the design in relief onone side and in intaglz'o on the other, and is ready for the productionJOSEPH BROWN.

Witnesses:

A. O. HENDERSON, W. F. WARREN.

